INSTALLING AND USING DOCKER ON SLACKWARE

2015-06-06

Docker

Imagine you want an asterisk system complete with mariadb and apache but you don't want to
install all that on your day-to-day system. You could create a VM. but vms are heavy and have quite some overhead.
What about backups? you can't copy live running image (not with qemu at least).

Enter Docker. Docker makes this really simple. Docker encloses an environment like a chroot would. But
it acts more like a vm. With docker, the equivalent of a vm is a container. You create your
filesystem and install the needed software in your container and run it. But Docker lets you run 1 command
only. You start the container, the command executes, in its environment, and the container stops. All this using
the host's kernel but separated with namespaces and cgroups. Nothing prevents you from running a script as the command.
So you make a script that starts httpd and asterisk then load bash. the container will run as long as bash doesn't exit.
so if you attach your session on the container and "exit" bash, the container will stop amd asterisk and httpd will shutdown.
The container does not start "init" (unless it's the command you chose to invoke) so it's not like an entire OS is
brought up. Only the command you run is ran in the container's FS but with the host's kernel

Docker allows you export running containers to a tarball. the tarball contains the entire FS of the container (not the memory)
You can then import it anywhere where Docker runs.

Installing docker on slackware

These are the instructions for installing docker 1.7.0 on slackware 14.1 with kernel 3.11.1.
I also tried with slackware 14.0 but the rc.S script does not mount the cgroup hierarchy properly
So I modified it to do it like in 14.1
I could not get it to work with kernel 3.10.17 and did not bother to troubleshoot since I had
a 3.11.1 on hand. 1.7.0-rc1 did not work for me. I needed commit 6cdf8623d52e7e4c5b5265deb5f5b1d33f2e6e95 in.
So I cloned the bleeding edge from git but then 2h later rc2 came out.

Pre-requisites

Before anything, you should make sure that your kernel is compiled with

Download, compile, and prepare the environment

At first, I tried downloading the binaries but docker was complaining about "Udev sync is not supported".
I found out that was because the binary is statically link and it causes some problems that I didn't care to look
into. So I opted for building from source. The first step is to get "go". I didn't want to leave this on my
system so I just put it in a temporary place and then deleted it.

wget https://storage.googleapis.com/golang/go1.4.2.linux-amd64.tar.gz
tar -zxf go1.4.2.linux-amd64.tar.gz
mv go /opt
#You should make that permanent if you intend to keep Go after building Docker
PATH=$PATH:/opt/go/bin
GOPATH=/opt/go:/opt/go/src/github.com/docker/docker/vendor
# download docker source.
wget https://github.com/docker/docker/archive/v1.7.0-rc2.tar.gz
tar -zxf v1.7.0-rc2.tar.gz
cd docker-1.7.0-rc2
#docker won't build because there is a header file that won't be found. There is a patch
#for that but let's do it manually here:
sed -i "/ioctl\.h/c\#include \r\n#include \r\n#include \r\n#include \r\n#include \r\n" daemon/graphdriver/btrfs/btrfs.go
#note that DOCKER_GIT_COMMIT needs to match the version you have downloaded
GOROOT=/opt/go AUTO_GOPATH=1 DOCKER_GITCOMMIT="395cced " ./hack/make.sh dynbinary
cp bundles/1.7.0-rc2/dynbinary/docker-1.7.0-rc2 /usr/sbin/docker
cp bundles/1.7.0-rc2/dynbinary/dockerinit-1.7.0-rc2 /usr/sbin/dockerinit
#remove go... or not. It's up to you. If you leave it there, you might want to permanently add it to your PATH
rm -Rf /opt/go

Prepare network bridge

In my case, since I was already using KVM/qemu, I had a bridge alrady setup.
But this is what would be needed

You might want that last example to run at boot time. There is a way to setup a bridge with the init scripts but I just added those lines in rc.local before launching the docker daemon.

There is currently no easy way to assign a static IP to your container. Docker will choose an IP
in the range of you bridge. But this isn't perfect. It seems to pick some addresses that are already used on my network. Issue 6743 on githubis opened for that.
But for the time being, I've hacked the code to make this possible. I won't create a pull request since
they are already working on a more elegant solution. But meanwhile, you can download my fork if you need it.
My fork on github.. That repo contains the patch
to build on slackware and also adds a "--ipv4-adress=A.B.C.D" option to docker run.

Auto start

Finally, you should add this in your rc.local script.

/usr/sbin/docker -d -b br0&

Building a container, running it and doing backups

My use case

What I'm looking to do is to isolate my home automation services in one container
that I can easily transport from one computer to another (or even to a VM). In case
I get a hardware failure, I want to reduce the downtime of my house services. Those include
Asterisk, httpd, MariadDB, CouchDB, DHAS, cron jobs,
and some more. I want to be able to make a daily backup of the container and always be able to
launch it from somehwere else where Docker is installed.

Creating a container

docker run vbatts/slackware:14.1 -ti /bin/bash

That command will create a container from a base image "slackware 14.1" from docker hub.
The image will be downloaded automatically. Then bash will be invoked. the -t -i flags
will give you an interactive TTY attached so you will be able to interact with bash.
From there, install whatever you need in the container. Download gcc, install it, etc. Once you
are done, exit bash. By exiting bash, the container stops. You can now commit your changes to a
new base image

docker commit ContainerID awesomeNewImage

Now you have a base image of your own that you can share with other people. Now create another container
for your real use case from the base image.

docker run -tid --restart=always awesomeNewImage /root/start.sh

The -d flag runs the contain in the background. You can access it using "docker attach".
--restart=always will make the container restart automatically when you exit it and when
the docker daemon starts (after a host reboot for example). When you were setting up
you base image, you could have created a start.sh script that invokes asterisk, httpd, mysqld and couchdb then bash.
To detach from the container without stopping it (leaving your command running) you can Ctrl-P, Ctrl-Q.

Backup/Restore

An easy way to backup is to regularly export the container (Cron job?).

docker export -o backup.tar

This will create a tarball container the entire filesystem of your container.
Then to restore, either locally or on some other machine runner docker:

cat backup.tar | docker import - restoredbackup

SYSTEM ON A CHIP EMULATOR

2015-04-09

I was looking at some online NES emulators the other day and it gave me an idea.
What If I created my own emulator but for my own architecture instead of emulating an
existing one? Of course that would be easier because I can decide what the architecture looks
like instead of having to go through the specs of the platform I want to emulate.
So I decided to create my own instructions with an assembler and a disassembler. The assembler
converts the assembly code to a binary format (obviously) and the result can be downloaded.
Again, this is my own virtual assembly and my own architecture so the instructions are encoded in
my own format. Each instructions are (inneficiently)encoded on 64bit including a references to 2 operands, 1 immediate 32bit value and a condition code. Each instruction is conditional.

USING JSSIP AND ASTERISK TO MAKE A WEBPHONE

2015-04-07

Building a web-based phone is easy enough with asterisk and jssip. At the time of writing this,
I was using asterisk 11.6 (LTS) and jssip 0.6.21.

My web application is hosted on a local webserver that resides on the same server as asterisk.
Because of that, it is not possible to tell asterisk to bond on port 80 or 443 for its
internal websocket server. So I've configured asterisk to bond on port 8088. But having a webapp
that wants to communicate on such a port will not work if the clien is behind a firewall that blocks
outside access to non standard ports. So I've configured Apache to proxy websocket connections to
a chosen URL to the asterisk server on the local host.

Configuring asterisk

step-by-step instructions:

Make sure res_srtp is loaded in asterisk (you may need to install libsrtp and rebuild asterisk).
This is absolutely needed for webrtc to work.

Building the SIP client

jssip is very easy to use. The following example should register to your server
and automatically answer an incoming call

C++ WEBSOCKET SERVER

2015-04-01

I recently wanted to learn a bit more about websockets. And by that, I don't mean how to use websockets from javascript
but rather how the server part works and what the protocol looks like. So I decided to write my own server library.
I followed RFC6455 but there is still some things I need to change in order to be fully compliant. There's not much
to say about the library other than it is very easy to use. I did try libwebsocket before. It is pretty complete but I
felt like it was a little more complicated than it should. So although my library is not as complete as libwebsocket, it
is easier to use and will be good enough for most of my projects.